1. Technical Field
The present invention relates to a process for producing 2-hydroxy-4-methylthiobutyric acid usable for a feed additive for animals.
2. Description of the Related Art
Conventionally, as a process for producing 2-hydroxy-4-methylthiobutyric acid have been known processes of hydration and hydrolysis reaction of 2-hydroxy-4-methylthiobutyronitrile in the presence of sulfuric acid (e.g., reference to EP-A-0142488, EP-A-0143100, U.S. Pat. No. 4,912,257, U.S. Pat. No. 5,976,609, WO 96/40630, U.S. Pat. No. 6,815,560, U.S. Pat. No. 6,743,946, WO 00/46190, WO 02/08181, EP-A-0863135, EP-A-1266885, JP-A-2002-255927, and JP-A-2002-293770). In these processes, generally after oil-water separation of hydration and hydrolysis reaction mixtures is carried out, the oil layer is concentrated to obtain 2-hydroxy-4-methylthiobutyric acid as a product.